1. Field of the Invention
The present invention relates to a bonding apparatus for bonding two parts such as a semiconductor chip and a substrate, lead frame or tab tape and more particularly to an optical detection device for detecting positional discrepancies between the two parts so as to make an alignment thereof.
2. Prior Art
For example, the apparatus disclosed in Japanese Patent Application Publication (Kokoku) No. H6-28272 is known as a conventional bonding apparatus that is equipped with an optical detection device. This optical detection device is comprised of an optical probe which is moved between two parts positioned so as to face each other for being bonded, first and second optical means which focus respective images of the two parts from the optical probe, and an image pickup means which pick up the images focused by the first and second optical means. The two parts are aligned based upon the detection results obtained by the optical detection device, and then bonding is performed for these two parts.
This apparatus will be described in more detail with reference to FIGS. 4 through 7.
As shown in FIG. 4, a substrate 1 is positioned and held by a substrate chuck 3 which is installed on an XY table 2, and a semiconductor chip 4 is held by a chip chuck 6 disposed on the bonding head 5. After the semiconductor chip 4 is moved to a point above the substrate 1, the bonding head 5 is lowered, and the chip 4 is bonded to the substrate 1. Here, the bonding head 5 is disposed on a supporting element 7 in a manner that the bonding head 5 can be raised and lowered. An optical detection device 10 is installed on an XY table 11 and moved between the substrate 1 and the semiconductor chip 4. The XY table 11 is mounted on the supporting element 7, and the optical detection device 10 has an optical probe which will be described later. Images of the substrate 1 and semiconductor chip 4 obtained by the optical detection device 10 are synthesized by an image synthesizing circuit 12 and displayed on a TV monitor 13.
As shown in FIG. 5, the optical detection device 10 comprises an optical probe 20 which is moved between the substrate 1 and the semiconductor chip 4, first and second optical means 25A and 25B and first and second illumination means 30A and 30B which are associated with the optical probe 20, and first and second image pickup means 35A and 35B for picking up the images which are of the substrate 1 and semiconductor 4 and focused by the first and second optical means 25A and 25B.
As seen from FIGS. 4 and 5, the optical probe 20 includes a first image acquisition prism 21A and a second image acquisition prism 21B. The first image acquisition prism 21A causes a 90-degree rotation of a first image of the surface of the semiconductor chip 4, e.g., an alignment mark applied to the semiconductor chip 4, a bump on the semiconductor chip 4 or the like. The second image acquisition prism 21B causes a 90-degree rotation of a second image of the surface of the substrate 1, e.g., an alignment mark applied to the substrate 1 or a pad on the substrate 1 in a different direction from the first image or the like. The optical probe 20 further includes a first optical system introduction prism 22A and a second optical system introduction prism 22B which are respectively provided on both sides of the first and second image acquisition prism 21A and 21B. The first image obtained by the first image acquisition prism 21A is reflected by the first optical system introduction prism 22A which causes a 90-degree reflection of the first image and then enters into a first optical means 25A. Likewise, the second image obtained by the second image acquisition prism 21B is reflected 90 degrees by the second optical system introduction prism 22B and enters into a second optical means 25B.
The above-described first and second illumination means 30A and 30B are perpendicularly disposed in respective positions between the first and second optical means 25A and 25B and first and second image pickup means 35A and 35B. Illuminating light beams produced by the first and second illumination means 30A and 30B are respectively projected (as projected light beams 32A and 32B) in the directions of the first and second optical means 25A and 25B by first and second half-mirrors 31A and 31B. These projected light beams 32A and 32B are respectively projected on the semiconductor chip 4 and substrate 1 via the first and second optical means 25A and 25B, first and second optical system introduction prisms 22A and 22B and first and second image acquisition prisms 21A and 21B.
The projected light 32A strikes the semiconductor chip 4, and thus becomes reflected light 33A. A first image (of the semiconductor chip 4) based on this reflected light 33A passes through the first image acquisition prism 21A, first optical system introduction prism 22A, first optical means 25A and first half-mirror 31A and is picked up by the first image pickup means 35A. The projected light 32B strikes the substrate 1, and thus becomes reflected light 33B. A second image (of the substrate 1) based on this reflected light 33B passes through the second image acquisition prism 21B, second optical system introduction prism 22B, second optical means 25B and second half-mirror 31B and is picked up by the second image pickup means 35B.
The first image of the downward-facing surface of the semiconductor chip 4 is caused to be incident on the first image acquisition prism 21A, and the second image of the upward-facing surface of the substrate 1 is caused to be incident on the second image acquisition prism 21B. Consequently, if the first and second images produced by the first and second image acquisition prisms 21A and 21B were merely reflected by the first and second optical system introduction prisms 22A and 22B, the images picked up by the first and second image pickup means 35A and 35B would not be in a relationship suitable for superimposition with the surface positions arranged in the corresponding image positions. Accordingly, as shown in FIGS. 4 and 6, the first image which is picked up by the first image pickup means 35A is reflected by an inverting mirror 40 so that a mirror image is formed and then picked up by the perpendicularly installed first image pickup means 35A.
The first and second images picked up by the first and second image pickup means 35A and 35B are synthesized by the image synthesizing circuit 12 shown in FIG. 5, and the synthesized images are shown on a TV monitor 13. Then, the XY table 2 is driven so that any positional discrepancies between the two images are corrected, thus aligning the two images. Afterward, the XY table 11 is driven so that the optical probe 20 of the optical detection device is withdrawn from between the substrate 1 and the semiconductor chip 4. Then, the bonding head 5 is lowered so that the semiconductor chip 4 is bonded to the substrate 1.
In the prior art described above, in order to place the two images in a relationship which is suitable for superimposition with surface positions arranged in the corresponding image positions, the first image is converted into a mirror image by an inverting mirror 40. Since the first and second image acquisition prisms 21A and 21B and first and second optical system introduction prisms 22A and 22B are provided in front of the first optical means 25A, there is no space to install an inverting prism 40 in this area. For this reason, the inverting mirror 40 is installed between the first optical means 25A and first image pickup means 35A as seen from FIG. 7.
As seen from the above, the prior art optical detection device 10 is designed so that the first image of the first optical means 25A is reflected by the inverting mirror 40, and this reflected first image is picked up by the first image pickup means 35A. Accordingly, the size of the of the optical detection device 10 needs to be large, and its structure is complicated. In addition, the optical detection device 10 repeatedly advances into and withdraws from the space between the substrate 1 held on the substrate chuck 3 and the semiconductor chip 4 held on the chip chuck 6 for every bonding operation; accordingly, if the optical detection device 10 is large, the XY table 11 must be also large so as to withstand a higher load. As a result, the size of the bonding apparatus increases, and the cost of the apparatus also increases. Furthermore, if the size of the XY table increases, the advancing and withdrawing stroke for each bonding are also increased, thus lowering the bonding speed; and in addition, the structure becomes further complicated, and deviations of the optical axis caused by heat, vibration and changes over time tend to occur, leading to a drop in the precision of detection.
Accordingly, the object of the present invention is to provide a bonding apparatus equipped with an optical detection device which is smaller than prior art optical detection devices.
The above object is accomplished by a unique structure of the present invention for a bonding apparatus which includes an optical detection device comprising: an optical probe which can be moved between first and second parts that are positioned to face each other so as to be bonded, first and second optical means which focus respective images of the first and second parts from the optical probe, and an image pickup means which pick up the images focused by the first and second optical means, so that bonding is performed after the first and second parts are aligned on the basis of the detection results obtained by the optical detection device, and in the present invention, the above-referred optical probe comprises: first and second image acquisition prisms which reflect first and second images of the first and second parts in different directions; a first optical system introduction prism or mirror which causes the first image of the first part that passes through the first image acquisition prism to be reflected an even number of times and then sends this first image to the first optical means; and a second optical system introduction prism or mirror which causes the second image of the second part that passes through the second image acquisition prism to be reflected an odd number of times and then sends this second image to the second optical means.
In the present invention, the above first optical system introduction prism is either a pentagonal prism, a roof prism, a 45-degree deflection prism which reflects twice, a 30-degree deflection prism which reflects twice, a Doubress""s prism which reflects four times, or a Porro prism which reflects four times; and any combination of these elements can be also employed.